The present invention relates to improvements in weight-responsive vehicle detection apparatus, and, in one particular aspect, to novel and improved electrical-switching type sensors of uncomplicated low-cost construction and of thin highly-elongated strip form which are highly rugged and will reliably make and break advantageously broad-area non-sliding contacts under both light and severe loadings, including those attended by transverse acceleration or braking forces, as the result of a unique compact low-profile cartridged construction involving an open-topped channel in which an edge-mounted narrow flexible upper switch blade is normally maintained in a very minute spacing from a contact strip below it by thin plastic edge spacer material, the upper blade being locally deflectable in response to vehicle tire loadings transmitted to it through a cast bed of flexible surfacing from which it is parted by a suitable film.
Vehicle sensors of a variety of types have been known heretofore, including those which rest upon or are recessed below a roadway for such purposes as signalling the presence of a vehicle, counting their numbers, or automatically actuating a barrier and/or ticket-dispensing machine at parking garages, toll highways and like places. Familiar examples are the cable-like pressure-responsive detectors used at most filling stations to signal attendants or temporarily draped across roadways to gather traffic data. When the detector installations are to be substantially permanent, they are expected to withstand the rigors of shock, vibration, and skid or tire-spin forces, as well as extremes of temperature, moisture and contamination, while nevertheless accurately and reliably sensing each application and removal of tire-induced loading by all vehicles from the lightest to heaviest of common weights. Earlier proposals have included simple electricaL contacting members, fluid-filled actuator tubes, and deformable members equipped with strain gages, and it has been known to implant such detectors below the level of a roadway within a yieldable mass, such as one of vulcanized rubber which is positioned essentially flush with the road surface.
In sophisticated vehicle-sensing systems, the detections may be required to exhibit a "logic" which can be employed by associated electronic circuitry to prevent drivers or attendants from interfering with the intended system functions, for such purposes as escaping a proper toll. A plurality of narrow elongated detectors, installed in spaced parallel relationship across a lane, can develop a pattern or logic of signals rendering a revenue-control system immune to such cheating, despite evasive vehicle maneuvers, but it then becomes quite important that the detector signals be positive, rapid and sharp. Simple electrical contacting or switching is theoretically appropriate, although in practice it is very difficult to make, hold and break connections cleanly and sensitively, and to avoid shortings or irregularities due to particle build-up resulting from wear; contact contaminations, particularly as a consequence of "pumping" actions within compressible switching cavities, are also a source of difficulty.
The improved and unusual vehicle-detection apparatus with which the present invention is concerned are also of the latter type, namely those in which electrical switching is effected, and in which such switching is of a quality and reliability appropriate to interfacing with revenue-control logic systems. Toward those ends, the sensors are rendered highly durable and resistant to extremes of loading and abuse, while at the same time being of mechanical nicety and operational sensitivity appropriate to ease of manufacture and reliability of signalling; moreover, electrical contacting is rendered substantially immune to wear, and very minute contact spacings, inherently promoted by the configuration and assembly of contacts, minimize difficulties brought on by pumping actions.